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Re: NMEA time oscillates
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From: |
Gary E. Miller |
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Subject: |
Re: NMEA time oscillates |
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Date: |
Fri, 12 Mar 2021 10:05:56 -0800 |
Yo Steven!
On Thu, 11 Mar 2021 22:48:17 -0600
Steven Sommars <stevesommarsntp@gmail.com> wrote:
> GPS: Uputronics RPi board [ublox] Rpi4.
> gpsd -n /dev/ttyS0 /dev/pps0 [Invoked by root from command line]
Good.
> Using gpsd 3.20 the NMEA offset (reported by ntpshmmon) is typically
> around 110 msec.
Why are you using NMEA on a u-blox baord?
> Using gpsd git head the NMEA offset oscillates between about 140 msec
> (duration ~440 sec) and then 580 msec (duration ~440 sec).
Normal.
> Resetting gps using ubxtool did not help.
Of course.
> I have no specific need to run git head, but this behavior surprised
> me.
Why? NMEA senences are variable length, and varying numbers of them
are sent every fix epoch. So that takes varying amounts of time to
get squeezed throught the serial pipe.
> Suggestions?
Chill. The PPS is keeping your time accurate, ignore the NMEA time.
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can't measure it, you can't improve it." - Lord Kelvin
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